Hitherto, as a pressure control valve used in a hydraulic circuit used for an industrial vehicle or the like, there is known a balance piston type relief valve illustrated in FIG. 5 as below. Such a pressure control valve a3 is provided between an input port a1c receiving a hydraulic liquid and a tank port aid communicating with a tank storing the hydraulic liquid and includes a main valve portion a4 which is formed by using a main valve body a6 and a valve accommodation body a7 including a main valve seat a7a on which the main valve body a6 sits and a pilot chamber a1b which accommodates the main valve body a6 in a slidable manner and a pilot valve portion a5 which is formed by using a pilot valve body a8 and a pilot valve seat member a9 which has a pilot valve seat a9a on which the pilot valve body a8 sits and is fixed to the valve accommodation body a7 of the main valve portion a4. The main valve body a6 and the pilot valve body a8 are all urged by urging members a101 and a102 to respectively sit on the main valve seat a7a and the pilot valve seat a9a. Then, when the main valve portion a4 and the pilot valve portion a5 are all switched to a valve closed state, a hydraulic pressure inside the input port a1c acts on the pilot valve body a8 through the back pressure chamber a6a of the main valve body a6.
Here, when a pressure inside the input port a1c becomes a predetermined value or more, a hydraulic pressure acting on the pilot valve body a8 overcomes an urging force generated by the urging member a102, the pilot valve body a8 is separated from the pilot valve seat a9a, and the pilot valve portion a5 is switched to a valve opened state. At this time, since the inside of the back pressure chamber a6a communicates with the tank port aid, a flow of the hydraulic liquid from the input port a1c toward the tank port aid occurs and thus the hydraulic liquid flows through the hole a6b of the main valve body a6. In response to the flow rate through the hole a6b, a differential pressure is generated between the inside of the input port a1c and the inside of the back pressure chamber a6a. Accordingly, since a force caused by the differential pressure overcomes an urging force generated by the urging member a101, the main valve body a6 is also separated from the main valve seat a7a and the main valve portion a4 is also switched to a valve opened state.
However, when the main valve portion a4 is switched to the valve opened state, the hydraulic liquid flows through a gap formed between the main valve body a6 and the main valve seat a7a. Since the flow of the hydraulic liquid is fast and unstable, a slight change in hydraulic liquid pressure occurs. For that reason, there is a case where chattering occurs due to a change in direction of a force applied to the main valve body. At that time, a problem arises in that a vibration or noise occurs inside the hydraulic circuit.
As one configuration for suppressing such a problem, a configuration in which a member for guiding an operation direction of the main valve body is provided outside the main valve body is considered (for example, see Patent Document 1). With such a configuration, since the operation direction of the main valve body at the time of opening the valve is guided, it is possible to prevent a collision between the main valve body and the valve accommodation body to a certain degree.
However, at the moment in which the main valve body is switched to the valve opened state, the magnitude of the force applied to the hydraulic liquid pressure suddenly changes and the direction of the force applied to the main valve body suddenly changes. At that time, since the main valve body suddenly moves, the main valve body suddenly collides with the valve accommodation body so that a problem such as a vibration or noise occurs inside the hydraulic circuit.